Non-reducing dielectric ceramic, monolithic ceramic capacitor using the same, and method for making non-reducing dielectric ceramic

ABSTRACT

A non-reducing dielectric ceramic contains Ca, Zr and Ti as metallic elements and does not contain Pb. In a CuKα X-ray diffraction pattern, the ratio of the maximum peak intensity of secondary crystal phases to the maximum peak intensity at 2θ=25° to 35° of a perovskite primary crystal phase is about 12% or less, the secondary crystal phases including all the crystal phases other than the perovskite primary crystal phase. The non-reducing dielectric ceramic exhibits superior insulating resistance and dielectric loss after firing in a neutral or reducing atmosphere and high reliability in a high-temperature loading lifetime test and is useful for producing compact high-capacitance monolithic ceramic capacitors.

This is a division of application Ser. No. 09/828,013, filed Apr. 6,2001 now U.S. Pat. No. 6,617,273.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to non-reducing dielectric ceramics,monolithic ceramic capacitors using the same, and methods for making thenon-reducing dielectric ceramics.

2. Description of the Related Art

In various electronic devices, the rapid trends toward a reduction insize and greater packing density are producing an increasing demand formonolithic ceramic capacitors which allow such trends to continue toadvance. Also, the use of the monolithic ceramic capacitors is beinginvestigated in other industrial fields, including for use in vehiclesand the like. Other desired requirements for the monolithic ceramiccapacitors include further reduction in cost and higher reliability.

The need to meet these requirements has promoted the development ofnon-reducing dielectric ceramic materials which use inexpensive basemetals as internal electrode materials, which are not changed intosemiconductive materials during firing in a neutral or reducingatmosphere with a low oxygen partial pressure so as not to oxidize theinternal electrode materials, and which exhibit superior dielectriccharacteristics.

For example, as non-reducing dielectric ceramic materials, JapaneseUnexamined Patent Application Publication Nos. 60-131708, 63-126117,5-217426, 10-335169, 10-330163, and 11-106259 disclose(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃-based,[(CaxSr_(1-x))O][(Ti_(y)Zr_(1-y))O₂]-based and(CaO)_(x)(Zr_(1-y)Ti_(y))O₂-based compositions.

The use of these non-reducing dielectric ceramic materials enablesproduction of inexpensive, reliable monolithic ceramic capacitors whichare not converted into semiconductive materials during firing inreducing atmospheres and which use base metals such as nickel and copperas internal electrodes.

In the non-reducing dielectric ceramics disclosed in Japanese UnexaminedPatent Application Publication Nos. 60-131708 and 63-126117, the maincomponent materials, e.g., calcium carbonate (CaCO₃), strontiumcarbonate (SrCO₃), titanium dioxide (TiO₂) and zirconium dioxide (ZrO₂),a subsidiary component material, e.g., manganese dioxide (MnO₂), and amineralizer, e.g., silicon dioxide (SiO₂), are simultaneously calcinedin order to prepare ceramics represented by(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃. The calcined raw material powderdoes not have a single perovskite structure, but, rather, has a mixedcrystal system containing a perovskite primary crystal phase and othersecondary crystal phases according to analysis by X-ray diffraction.Also, a dielectric ceramic obtained by firing this calcined raw materialpowder in a reducing atmosphere has a mixed crystal system. Such annon-homogeneous crystal structure in the dielectric ceramic tends toreduce the reliability of devices as the thickness of the ceramic isreduced to produce compact high-capacitance monolithic ceramiccapacitors when they are subjected to high-temperature loading lifetimetesting.

In the non-reducing dielectric ceramics disclosed in Japanese UnexaminedPatent Application Publication Nos. 5-217426 and 10-335169, powders ofcalcium titanate (CaTiO₃), strontium titanate (SrTiO₃), strontiumzirconate (SrZrO₃) and calcium zirconate (CaZrO₃) are used as startingmaterials in order to prepare ceramics represented by(Ca_(1-x)Sr_(x))_(m)(Zr_(1-y)Ti_(y))O₃ and[(Ca_(x)Sr_(1-x))O][(Ti_(y)Zr_(1-y))O₂]. After weighing these powders,the resulting ceramic is obtained through wet mixing, molding, binderremoval and firing. In this method, however, CaTiO₃, SrTiO₃, SrZrO₃ andCaZrO₃ having perovskite structures barely dissolve into each other.Therefore, the resulting dielectric ceramic has a mixed crystal systemincluding a plurality of perovskite crystal phases. When the thicknessof the elements is reduced to produce compact high-capacitancemonolithic ceramic capacitors, the lifetimes of the monolithic ceramiccapacitors in a high-temperature loading lifetime test vary and thereliability thereof tends to be impaired.

In the non-reducing dielectric ceramics disclosed in Japanese UnexaminedPatent Application Publication Nos. 10-330163 and 11-106259,predetermined amounts of calcium carbonate (CaCO₃), titanium dioxide(TiO₂), zirconium dioxide (ZrO₂) and manganese carbonate (MnCO₃) areused as starting materials, a predetermined amount of glass component isused, and these are mixed, molded, subjected to binder removal and firedin order to prepare ceramics represented by (CaO)_(x)(Zr_(1-y)Ti_(y))O₂.In this method, however, the formation of a perovskite crystal phase asthe primary crystal phase is impaired and the resulting dielectricceramic has a mixed crystal system including the perovskite primarycrystal phase and other secondary crystal phases. When the thickness ofthe elements is reduced to produce compact high-capacitance monolithicceramic capacitors, the reliability of the monolithic ceramic capacitortends to be reduced.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anon-reducing dielectric ceramic which does not cause deterioration ofinsulating resistance and dielectric loss during firing in a neutral orreducing atmosphere, and which exhibits a prolonged lifetime with areduced variation in high-temperature loading lifetime testing when thethickness of the elements is reduced, and high reliability.

It is another object of the present invention to provide a monolithicceramic capacitor using the non-reducing dielectric ceramic. It is stillanother object of the present invention to provide a method for making anon-reducing dielectric ceramic.

A non-reducing dielectric ceramic according to the present inventioncomprises Ca, Zr and Ti as metallic elements and does not contain Pb. Ina CuKα X-ray diffraction pattern, the ratio of the maximum peakintensity of secondary crystal phases to the maximum peak intensity at2θ=25° to 35° of a perovskite primary crystal phase is about 12% orless, wherein the secondary crystal phases include all the crystalphases other than the perovskite primary crystal phase. The ceramic maybe represented by A_(p)BO₃ where A includes Ca, B includes Zr and Ti,and p is about 0.98 to 1.02.

The ratio of the maximum peak intensity of the secondary crystal phasesto the maximum peak intensity of the perovskite primary crystal phase ispreferably about 5% or less and more preferably about 3% or less.

Since the ratio of the maximum peak intensity of the secondary crystalphases to the maximum peak intensity of the perovskite primary crystalphase is about 12% or less, the secondary crystal phase content in theoverall crystal phases is low. Thus, the resulting dielectric ceramicdoes not cause deterioration of insulating resistance and dielectricloss during firing in a neutral or reducing atmosphere, and exhibits aprolonged lifetime with a reduced variation in high-temperature loadinglifetime testing when the thickness of the dielectric ceramic layer isreduced to about 5 mm or less and high reliability.

A monolithic ceramic capacitor in accordance with the present inventioncomprises a plurality of dielectric ceramic layers, internal electrodesprovided between dielectric ceramic layers and external electrodeselectrically connected to the internal electrodes, wherein thedielectric ceramic layers comprise the above-mentioned dielectricceramic and the internal electrodes comprise a base metal. The basemetal is preferably elemental nickel, a nickel alloy, elemental copperor a copper alloy.

Since the monolithic ceramic capacitor in accordance with the presentinvention uses the above-mentioned non-reducing dielectric ceramic, themonolithic ceramic capacitor does not cause deterioration of insulatingresistance and dielectric loss during firing in a neutral or reducingatmosphere, and exhibits a prolonged lifetime with a reduced variationin high-temperature loading lifetime testing when the thickness of thedielectric ceramic layer is reduced to about 5 μm or less, and highreliability.

In a method for making a non-reducing dielectric ceramic comprising Ca,Zr and Ti as metallic elements and not containing Pb, and in a CuKαX-ray diffraction pattern, the ratio of the maximum peak intensity ofsecondary crystal phases to the maximum peak intensity at 2θ=25 to 35°of a perovskite primary crystal phase is about 12% or less, wherein thesecondary crystal phases include all the crystal phases other than theperovskite primary crystal phase, the method comprises the steps of:

(A) calcining an uncalcined B-site component powder to prepare acalcined B-site component powder, wherein the dielectric ceramic isrepresented by the general formula ABO₃;

(B) preparing a A-site component powder from A-site component materials;

(C) mixing the B-site component powder and the A-site component powderto prepare an uncalcined primary material powder;

(D) calcining the uncalcined primary material powder to prepare acalcined primary material powder;

(E) adding at least one of the A-site component powder and the B-sitecomponent powder to the calcined primary material powder for finelyadjusting the composition of the calcined primary material powder toprepare a secondary material powder; and

(F) molding and firing the secondary material powder in a neutral orreducing atmosphere.

This method can produce dielectric ceramics with high reproducibilityand high efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an X-ray diffraction pattern of a dielectric ceramicof Sample 24;

FIG. 2 illustrates an X-ray diffraction pattern of a dielectric ceramicof Sample 23;

FIG. 3 illustrates an X-ray diffraction pattern of a dielectric ceramicof Sample 43; and

FIG. 4 illustrates an X-ray diffraction pattern of a dielectric ceramicof Sample 54.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to thefollowing non-limiting Examples.

EXAMPLE 1

Powders of CaCO₃, SrCO₃, BaCO₃, ZrO₂, TiO₂ and HfO₂, each having apurity of 99% or more, were prepared as starting materials.

ZrO₂, TiO₂ and HfO₂ were weighed as raw material powders for the B-sitecomponent in the perovskite primary crystal phase represented by ABO₃,such that x and y in the formula (Zr_(1-x-y)Ti_(x)Hf_(y))O₃ became thevalues shown in Table 1. These raw material powders were wet-mixed andpulverized in a ball mill for at least 16 hours and were dried toprepare an uncalcined B-site component powder.

Each uncalcined B-site component powder was calcined at each of thetemperatures shown in Table 1 for 1 to 2 hours in air to prepare acalcined B-site component powder.

Next, CaCO₃, SrCO₃ and BaCO₃ were weighed as raw material powders forthe A-site component so that v, w and k in the formula

(Ca_(1-v-w)Sr_(v)Ba_(w))_(k)(Zr_(1-x-y)Ti_(x)Hf_(y))O₃

became the values shown in Table 1.

These raw material powders for the A-site component were added to thecalcined B-site component to prepare an uncalcined primary materialpowder. The uncalcined primary material powder was wet-mixed andpulverized for at least 16 hours in a ball mill, dried and calcined at1,000° C. to 1,200° C. for 2 hours in air to prepare a calcined primarymaterial powder. The resulting calcined primary material powder had anaverage particle diameter of about 0.8 μm or less.

In Sample 34 in Table 1, CaZrO₃ and SrTiO₃ which had perovskite crystalstructures were used as starting materials. These materials were weighedbased on the formulation shown in Table 1 and were wet-mixed to preparea primary material powder containing the A-site and B-site componentswithout calcination.

In order to finely adjust the composition, CaCO₃, SrCO₃, BaCO₃, ZrO₂,TiO₂ and HfO₂ were weighed so that the p value in the formula(Ca_(1-v-w)Sr_(v)Ba_(w))_(p)(Zr_(1-x-y)Ti_(x)Hf_(y))O₃ became the valuesshown in Table 1 and were added to 100 mole of the calcined primarymaterial powder of each of Samples 1 to 34. Secondary material powdershaving finely adjusted compositions of the formula(Ca_(1-v-w)Sr_(v)Ba_(w))P(Zr_(1-x-y)Ti_(x)Hf_(y))O₃ were therebyprepared.

Then, in order to prepare a secondary material powder containing a MnOsubsidiary component, MnCO₃ having a purity of 99% or more was weighedand added to each secondary material powder so that 2 moles of MnO waspresent with respect to 100 mole of the secondary material powder.

To 100 parts by weight of secondary material powder containing MnO,either a sintering auxiliary (Sintering Auxiliary A) composed of 25% byweight Li₂O, 2% by weight MgO, 6% by weight CaO, 6% by weight SrO, 6% byweight BaO, 48% by weight SiO₂, 5% by weight TiO₂ and 2% by weight Al₂O₃or a sintering auxiliary (Sintering Auxiliary B) composed of 36% byweight (Si_(0.98)Ti_(0.02))O₂, 55% by weight (Mn_(0.8)Ni_(0.2))O and 9%by weight CaO was added in an amount of 1 part by weight so as toprepare formulated powders.

TABLE 1 Calcined Primary Material Powder Particle Size of FiringTemperature of Composition of Composition Uncalcined B-Site UncalcinedB-Site Formulated Material(Ca_(1−v−w)Sr_(v)Ba_(w))_(k)(Zr_(1−x−y)Ti_(x)Hf_(y))O₃ ComponentComponent Sintering Sample v w x y k (μm) (° C.) p Auxiliary 1 0.01 00.01 0.01 0.985 0.10 1150 0.990 A 2 0.01 0 0.01 0.01 0.995 0.07 11501.000 A 3 0.01 0 0.01 0.01 0.990 0.10 1150 0.995 A 4 0.01 0 0.01 0.010.990 0.10 1150 0.995 B 5 0.01 0 0.01 0.01 0.975 0.15 1150 1.000 A 60.01 0 0.01 0.01 0.990 0.12 900 1.000 A 7 0.01 0 0.01 0.01 0.930 0.351150 0.980 A 8 0.01 0 0.01 0.01 1.020 0.20 1100 1.020 A 9 0.01 0 0.010.01 0.950 0.10 1150 0.940 A 10 0.01 0 0.01 0.01 0.990 0.10 1150 1.040 A11 0.05 0.08 0.05 0.02 0.990 0.15 1100 1.000 A 12 0.05 0.08 0.05 0.020.990 0.14 1100 1.000 B 13 0.05 0.08 0.05 0.02 0.995 0.10 1100 1.010 A14 0.05 0.08 0.05 0.02 0.940 0.40 1100 0.995 A 15 0.04 0.33 0.04 0.010.980 0.20 1100 0.995 B 16 0.04 0.33 0.04 0.01 0.980 0.20 1100 0.995 A17 0.04 0.33 0.04 0.01 0.985 0.10 1150 1.000 A 18 0.04 0.33 0.04 0.010.985 0.08 900 0.995 A 19 0 0.01 0.40 0.01 0.970 0.30 1200 0.990 A 20 00.01 0.40 0.01 0.980 0.15 1150 0.990 A 21 0 0.01 0.40 0.01 0.980 0.151150 0.990 B 22 0 0.01 0.40 0.01 0.980 0.15 1150 0.995 A 23 0 0.01 0.400.01 0.950 0.35 1150 0.950 A 24 0.15 0.01 0.02 0.01 0.998 0.15 11501.000 A 25 0.15 0 0.29 0.01 0.975 0.25 1100 0.980 A 26 0.15 0 0.29 0.010.990 0.10 1050 0.995 A 27 0.15 0 0.29 0.01 0.975 0.15 1050 1.000 A 280.15 0 0.29 0.01 0.975 0.15 1050 1.000 B 29 0.15 0 0.29 0.01 0.975 0.151100 0.940 A 30 0 0 0.27 0.01 1.000 0.25 1150 1.030 A 31 0 0 0.27 0.010.990 0.09 1150 1.000 A 32 0 0 0.27 0.01 0.990 0.12 1100 0.995 A 33 0 00.27 0.01 0.970 0.40 1100 0.990 A 34 0.20 0 0.20 0.01 — — — 0.995 A

The formulated powders were wet-mixed with a polyvinyl butyral binderand an organic solvent such as ethanol for at least 16 hours in a ballmill to prepare ceramic slurries. From each ceramic slurry, a sheet wasformed by the doctor blade method and was cut into rectangular ceramicgreen sheets, each having a thickness of about 5 μm.

The ceramic green sheets were laminated and were bonded by thermalcompression to form ceramic green laminates. Each ceramic green laminatewas shaped into a rectangle having a predetermined size, heated to 350°C. in a nitrogen atmosphere to burn out the binder and fired at thetemperatures shown in Table 2 in a hydrogen-nitrogen-water reducingatmosphere to form a ceramic sintered compact.

TABLE 2 Ratio of Maximum Time to Failure Firing Intensity of DielectricSpecific of First Failed Temperature Secondary Crystal Loss Inductive CRProduct TC MTTF m Sample Sample (° C.) Phases (%) (%) Capacity (Ω · F)(ppm/° C.) (hour) Value (hours) 1 1250 <1.0 0.01 30 125000 +4 550 3.5460 2 1300 1.0 0.01 31 64000 +28 540 2.5 310 3 1250 <1.0 0.01 30 420000+5 460 3.2 285 4 1280 1.0 0.01 31 445000 +8 510 3.7 370 5 1300 1.5 0.0131 345000 +10 480 4.1 420 6 1300 12.5 0.11 31 214000 −1 655 0.5 90 71300 13.0 0.01 31 250000 +2 160 0.8 10 8 1350 13.5 0.15 28 70000 +24 7800.4 20 9 1250 16.0 0.02 30 59000 −15 90 2.1 5 10 1350 Not Sintered 111200 1.5 0.02 40 28000 −180 420 3.3 300 12 1250 2.0 0.03 41 28000 −175475 3.4 375 13 1250 3.5 0.02 41 12000 −160 305 2.1 140 14 1200 12.5 0.0339 8000 −175 330 0.6 5 15 1290 3.5 0.03 34 14000 −395 410 3.8 310 161250 4.0 0.04 34 11000 −400 375 4.1 315 17 1250 6.5 0.02 33 10000 −385310 2.2 165 18 1300 13.0 0.25 33 4500 −360 410 0.4 10 19 1280 1.5 0.0287 392000 −980 345 3.2 245 20 1280 2.5 0.02 85 350000 −985 380 3.5 30021 1300 2.0 0.01 86 450000 −1000 420 3.7 350 22 1300 <1.0 0.01 82 70000−950 320 2.8 225 23 1300 16.0 0.20 81 51000 −950 20 1.8 1 24 1280 7.10.01 34 680000 −11 520 3.8 380 25 1260 6.0 0.02 69 200000 −740 300 1.7120 26 1260 2.0 0.02 70 250000 −740 350 2.8 235 27 1280 1.5 0.02 70180000 −755 410 2.6 230 28 1290 1.0 0.01 69 285000 −765 455 3.3 355 291300 14.5 0.03 73 90000 −760 35 2.3 3 30 1350 Not Sintered 31 1300 1.50.02 46 81000 −700 415 3.8 325 32 1300 1.0 0.02 46 78000 −690 365 3.2280 33 1250 2.5 0.02 47 102000 −720 330 2.9 200 34 1250 30.0 0.01 5626000 −620 35 1.8 1

The ceramic sintered compact was pulverized with a mortar for powderCuKα X-ray diffractometry. In the X-ray diffraction pattern, the ratioof the maximum peak intensity of secondary crystal phases to the maximumpeak intensity at 2θ=25° to 35° of the perovskite primary crystal phasewas determined at a tube voltage of 40 kV and a tube current of 200 mA,wherein the secondary crystal phases include all the crystal phasesother than the perovskite primary crystal phase.

Monolithic ceramic capacitors were formed as follows. A conductive pasteprimarily composed of Ni was applied by printing onto theabove-mentioned ceramic green sheets to form conductive paste layers forconstituting internal electrodes extending to one edge of the sheet.

The resulting ceramic green sheets provided with the conductive pastelayers were laminated so that conductive paste layers were alternatelyexposed at opposing sides of the laminate. A ceramic green sheetlaminate was thereby formed.

The ceramic green sheet laminate was cut into rectangles having apredetermined size, heated to 350° C. in a nitrogen atmosphere to burnout the binder and fired in a hydrogen-nitrogen-water reducingatmosphere to form a monolithic ceramic sintered compact.

An external electrode paste was coated onto the two sides of theresulting monolithic ceramic compact at which internal electrodes wereexposed and was fired at a temperature of 600 to 800° C. in a nitrogenatmosphere to form a monolithic ceramic capacitor provided with externalelectrodes electrically connected to the internal electrodes. Ifnecessary or desired, a coating layer can be formed on the surfaces ofthe external electrodes by plating or the like.

The resulting monolithic ceramic capacitor had a width of 1.6 mm, alength of 3.2 mm and a thickness of 1.2 mm; the thickness of thedielectric ceramic layer was 3 μm; and the number of the effectivedielectric ceramic layers was 80.

Electrical properties of the monolithic ceramic capacitor were measured.The electrostatic capacitance and the dielectric loss were measured at afrequency of 1 MHZ and a temperature of 25° C. to calculate the specificinductive capacity. The insulating resistance was measured by a DCvoltage of 50V which was applied to the monolithic ceramic capacitor at25° C. for 2 minutes to calculate the CR product.

The changes in the electrostatic capacitance with temperature at afrequency of 1 MHZ were measured at 125° C. and 25° C. and the rate ofchange thereof (TC) was calculated based on equation (1):

TC={(C125−C25)/C25)}×{1/(125−25)}×10⁶ [ppm/° C.]  (1)

wherein C125 and C25 denote the electrostatic capacitances (pF) at 125°C. and 25° C., respectively.

In the high-temperature loading lifetime test, a DC voltage of 200 V wasapplied to 72 samples of each monolithic ceramic capacitor at atemperature of 150° C. to measure changes in insulating resistance overtime. The lifetime was defined as the time at which the insulatingresistance of the sample became 10⁶ Ω or less. The mean time to failure(MTTF) and the shape parameter m, which was an index of the variation inreliability, were calculated based on the Weibull probabilitydistribution. Also, the time to failure of the first failed sample wasrecorded. The results are shown in Table 2.

Table 2 demonstrates that in the non-reducing dielectric ceramic layerof each of the monolithic ceramic capacitors of Samples 1 to 4, 11 to13, 15 to 17, 19 to 22, 24 to 28 and 31 to 33, the ratio of the maximumpeak intensity of secondary crystal phases to the maximum peak intensityat 20=25° to 35° of a perovskite primary crystal phase is about 12% orless in the X-ray diffraction pattern measured using the CuKα rays,wherein the secondary crystal phases include all the crystal phasesother than the perovskite primary crystal phase.

Each monolithic ceramic capacitor exhibits a large CR product (theproduct of the electrostatic capacitance and the insulating resistance)of at least 1,000, a dielectric loss of 0.1% or less and a small rate ofchange in electrostatic resistance with temperature (TC) of −1,000 ppm/°C. or less. The mean time to failure (MTTF) in the high-temperatureloading lifetime test at 150° C. and 200 V is as long as 300 hours ormore. The lifetime of the first failed sample is long and the variationin the lifetime between samples is small, exhibiting high reliability.

The basis for the ratio of the maximum peak intensity of about 12% orless of the secondary crystal phases to the maximum peak intensity at20=25° to 35° of the perovskite primary crystal phase in the X-raydiffraction pattern will now be described.

At a ratio of the maximum peak intensity of the secondary crystal phasesto the maximum peak intensity of the perovskite primary crystal phaseexceeding about 12%, the monolithic ceramic capacitor exhibits adielectric loss of as high as 0.11 to 0.25% and a lifetime of as low as10 to 90 hours for the first failed sample, as shown in Samples 6, 8 and18. Alternatively, the lifetime of the first failed monolithic ceramiccapacitor is as low as 5 to 10 hours in Samples 7 and 14, although thedielectric loss thereof does not increase. Moreover, the MTTF is asshort as 20 to 90 hours and the lifetime of the first failed sample is 1to 5 hours in Sample 9, 23, 29 and 34. Accordingly, these samplesexhibit large variations in lifetime and deterioration of electricalproperties within relatively short periods.

In contrast, at ratio of the maximum peak intensity of the secondarycrystal phases to the maximum peak intensity of the perovskite primarycrystal phase of about 12% or less, the dielectric loss can besuppressed to 0.1% or less due to the small content of the secondarycrystal phases, resulting in improved electrical properties in thehigh-temperature loading lifetime test. In detail, the MTTF is at least300 hours and the lifetime of the first failed sample is at least 120hours with a reduced variation in the lifetime, exhibiting highreliability of the monolithic ceramic capacitors.

The non-reducing dielectric ceramic layer may contain impurities, suchas aluminum, iron and magnesium. Moreover, CoO, NiO, FeO, Al₂O₃, MgO,Sc₂O₃ and rare earth oxides including Y₂O₃ may be added as thesubsidiary components in addition to the above-described MnO, as long asthe ratio of the maximum peak intensity of the secondary crystal phasesto the maximum peak intensity of the perovskite primary crystal phase isabout 12% or less in the X-ray diffraction pattern.

In such cases, the resulting monolithic ceramic capacitors also exhibitsuperior electrical properties.

FIG. 1 illustrates the X-ray diffraction pattern of the dielectricceramic in the monolithic ceramic capacitor of Sample 24, in which theratio of the maximum peak intensity of the secondary crystal phases tothe maximum peak intensity of the perovskite primary crystal phase is7.1%. FIG. 2 illustrates an X-ray diffraction pattern of the dielectricceramic in the monolithic ceramic capacitor of Sample 23, in which theratio is 16.0%. In these drawings, peaks with asterisks (*) are assignedto the perovskite primary crystal phase and the other peaks are assignedto the secondary crystal phases.

The average particle diameter of the uncalcined B-site component powderis preferably about 0.5 μm or less and more preferably about 0.3 μm. Thelower limit thereof is not limited and is preferably about 0.01 μm orless.

As a first reason for limiting the particle size, an average particlediameter exceeding about 0.5 mm precludes a solid phase reaction, thatis, synthesis of (Zr_(1-x-y)Ti_(x)Hf_(y))₂O₄ in the calcined B-sitecomponent powder, resulting in large amounts of residual ZrO₂, TiO₂ andHfO₂. When this calcined B-site component powder is used, the perovskitecrystal phase (primary crystal phase) is insufficiently synthesizedduring calcination of the B-site component powder with the A-sitecomponent powder. However, secondary crystal phases are readily formed.

As a second reason, the formation of the solid solution of the secondarycrystal phases and the primary crystal phases is insufficient in adielectric ceramic using the calcined primary material powder due to theinsufficient synthesis of the primary crystal phase, and the secondarycrystal phases also remains after the calcination. Thus, the dielectricceramic has an inhomogeneous crystal structure which causes a largevariation in time to failure in the high-temperature loading lifetimetest of the monolithic ceramic capacitor.

The B-site component powder is preferably calcined at a temperature ofabout 1,050 to 1,200° C. for 1 to 2 hours, since the solid phasereaction for forming (Zr_(1-x-y)Ti_(x)Hf_(y))₂O₄ barely proceeds at acalcination temperature below about 1,050° C. in the B-site componentpowder. When the calcination temperature exceeds about 1,200° C., theaverage particle diameter of the calcined B-site component undesirablyincreases regardless of the high degree of synthesis of(Zr_(1-x-y)Ti_(x)Hf_(y))₂O₄ Such a calcined B-site powder precludes thesolid phase reaction during calcination with the A-site componentpowder, resulting in an insufficient formation of the perovskite primarycrystal phase.

In the composition(Ca_(1-v-w)Sr_(v)Ba_(w))_(k)(Zr_(1-x-y)Ti_(x)Hf_(y))O₃ of the calcinedprimary material powder, the k value is in the range of preferably0.95≦k<1.00 and more preferably 0.975≦k≦0.995. At a k value below about0.95, excessive grain growth occurs during calcination resulting in anincrease in the average particle diameter of the calcined primarymaterial powder. At a k value exceeding about 1.00, the formation of theperovskite primary crystal phase does not proceed sufficiently duringthe calcination of the primary material powder.

In the composition(Ca_(1-v-w)Sr_(v)Ba_(w))_(p)(Zr_(1-x-y)Ti_(x)Hf_(y))O₃ of the secondarymaterial powder, the p value is preferably in the range of 0.98≦p≦1.02and more preferably 0.99≦p≦1.01. At a p value below about 0.98, thesecondary crystal phases in addition to the perovskite primary phase areformed in the crystal structure of the sintered dielectric ceramic. Theformation of the secondary crystal phases contributes to the reductionin reliability of the monolithic ceramic capacitors in thehigh-temperature loading lifetime test when the thickness of thedielectric ceramic layer therein is about 5 μm or less. A p valueexceeding about 1.02 significantly precludes the formation of theperovskite primary crystal phase and sinterability, resulting inunsuccessful sintering of the composition and deterioration ofreliability of the monolithic ceramic capacitor.

In this example, elemental nickel was used in the internal electrode ofthe monolithic ceramic capacitor. A nickel alloy also has the sameeffects.

EXAMPLE 2

The same materials as those in Example 1 were used to prepare calcinedprimary material powders, each having the perovskite structure ABO₃ andcomposed of a A-site component and a B-site component. The primarymaterial powder of Sample 54 was prepared by wet-mixing withoutcalcination predetermined amounts of CaZrO₃, SrTiO₃ and BaZrO₃ havingperovskite crystal structures based on the formulation shown in Table 3.

In order to prepare secondary material powders, CaCO₃, SrCO₃, BaCO₃,ZrO₂, TiO₂ and HfO₂ were added to 100 mols of primary material powdersof Samples 41 to 54 so that the samples had p values shown in Table 3 inthe composition MnCO₃ having a purity of at least 99% was added to thesecondary material powders to prepare a secondary material powdercontaining a MnO secondary component so that the MnO content was 4 molesper 100 moles of the secondary material powders.

To 100 parts by weight of secondary material powder containing MnO, asintering auxiliary (Sintering Auxiliary C) composed of 60% by weightBaO, 5% by weight Li₂O, 15% by weight Ba₂O₃ and 20% by weight SiO₂ wasadded in an amount of 10 parts by weight so as to prepare formulatedpowders.

TABLE 3 Calcined Primary Material Powder Particle Size of FiringTemperature of Composition of Composition Uncalcined B-Site UncalcinedB-Site Formulated Material(Ca_(1−v−w)Sr_(v)Ba_(w))_(k)(Zr_(1−x−y)Ti_(x)Hf_(y))O₃ ComponentComponent Sintering Sample v w x y k (μm) (° C.) p Auxiliary 41 0.02 00.02 0.01 0.985 0.10 1150 0.990 C 42 0.02 0 0.02 0.01 0.995 0.07 11501.000 C 43 0.02 0 0.02 0.01 0.990 0.10 1150 0.995 C 44 0.02 0 0.02 0.010.990 0.10 1250 1.000 C 45 0.02 0 0.02 0.01 0.930 0.35 1150 1.000 C 460.02 0 0.02 0.01 0.990 0.10 1100 1.040 C 47 0.05 0.08 0.05 0.02 0.9900.15 1150 1.000 C 48 0.05 0.08 0.05 0.02 0.980 0.14 1150 1.005 C 49 0.050.08 0.05 0.02 0.940 0.40 1150 0.985 C 50 0 0.01 0.40 0.01 0.980 0.11900 0.990 C 51 0 0.01 0.40 0.01 0.980 0.15 1150 0.990 C 52 0 0.01 0.400.01 0.995 0.09 1150 0.995 C 53 0 0.01 0.40 0.01 0.970 0.15 1150 0.970 C54 0.06 0.09 0.06 0.02 — — — 0.995 C

As in EXAMPLE 1, ceramic slurries were prepared using these formulatedpowders, and a sheet was formed using each ceramic slurry and was cutinto rectangular ceramic green sheets having the same thickness as thatin EXAMPLE 1.

Ceramic sintered compacts were prepared using these ceramic green sheetsas in EXAMPLE 1.

The ceramic sintered compact was pulverized with a mortar for powderCuKα X-ray diffractometry, as in EXAMPLE 1. In the X-ray diffractionpattern, the ratio of the maximum peak intensity of secondary crystalphases to the maximum peak intensity at 2θ=25° to 35° of the perovskiteprimary crystal phase was determined as in EXAMPLE 1.

Monolithic ceramic capacitors were formed as follows. A conductive pasteprimarily composed of Cu was applied by printing onto theabove-mentioned ceramic green sheets to form conductive paste layers forconstituting internal electrodes.

The resulting ceramic green sheets provided with the conductive pastelayers were laminated as in EXAMPLE 1 to form a ceramic green sheetlaminate.

The ceramic green sheet laminate was cut into rectangles having apredetermined size, and a conductive paste primarily composed of Cu asan external electrode paste was applied onto the two sides of thelaminate at which the conductive paste within the laminate was exposed.After the binder in the laminate was burned out, the laminate was firedin a reducing atmosphere as in EXAMPLE 1 to form a monolithic ceramicsintered compact.

The resulting monolithic ceramic capacitor had the same dimensions asthose in EXAMPLE 1, the thickness of the dielectric ceramic layer was 4μm and the number of the effective dielectric ceramic layers was 80.Electrical properties of the monolithic ceramic capacitor were measuredas in EXAMPLE 1. These results are shown in Table 4.

TABLE 4 Ratio of Maximum Time to Failure Firing Intensity of DielectricSpecific of First Failed Temperature Secondary Crystal Loss Inductive CRProduct TC MTTF m Sample Sample (° C.) Phases (%) (%) Capacity (Ω · F)(ppm/° C.) (hour) Value (hours) 41 950 9.5 0.01 29 62000 +4 410 3.5 28542 980 10.5 0.02 29 40000 +28 345 2.5 140 43 950 11.0 0.01 28 55000 +5360 3.2 205 44 980 12.5 0.01 27 35000 +10 480 0.9 30 45 970 14.0 0.01 2916000 −1 360 0.8 15 46 1020 Not Sintered 47 1000 6.0 0.01 38 21000 −180390 2.7 235 48 1000 8.5 0.01 37 12000 −160 310 2.1 125 49 1000 15.0 0.0339 6000 −175 75 2.4 15 50 1000 13.0 0.05 78 5000 −990 240 0.9 15 51 10004.0 0.02 81 25000 −985 380 3.8 330 52 1000 3.5 0.03 80 12000 −995 3052.2 185 53 1000 18.0 0.20 82 1500 −980 30 1.5 5 54 1000 29.0 0.02 4035000 −180 220 0.4 2

Table 4 demonstrates that in the non-reducing dielectric ceramic layerof each of the monolithic ceramic capacitors of Samples 41 to 43, 47 to48 and 51 to 52, the ratio of the maximum peak intensity of secondarycrystal phases to the maximum peak intensity at 2θ=25° to 35° of aperovskite primary crystal phase is about 12% or less in a CuKα X-raydiffraction pattern, wherein the secondary crystal phases include allthe crystal phases other than the perovskite primary crystal phase.

Each monolithic ceramic capacitor exhibits a large CR product (theproduct of the electrostatic capacitance and the insulating resistance)of at least 1,000, a dielectric loss of 0.1% or less and a small rate ofchange in electrostatic resistance with temperature (TC) of −1,000 ppm/°C. or less. The mean time to failure (MTTF) in the high-temperatureloading lifetime test at 150° C. and 200 V is as long as 300 hours ormore. The lifetime of the first failed sample is long and the variationin the lifetime between the samples is small, exhibiting highreliability.

At a ratio of the maximum peak intensity of the secondary crystal phasesto the maximum peak intensity of the perovskite primary crystal phaseexceeding about 12%, the monolithic ceramic capacitor does not exhibitsuperior electrical properties, as shown in Samples 44, 45, 49, 50, 53and 54. That is, in Samples 44 and 45, the lifetime of the first failedmonolithic ceramic capacitor is as low as 15 to 30 hours and thelifetime varies between the samples, although the MTTF is as long as 360to 480 hours in the high-temperature loading lifetime test. Moreover,the MTTF is as short as 30 to 240 hours and the lifetime of the firstfailed sample ranges from 2 to 15 hours in Samples 49, 50, 53 and 54.Accordingly, these samples exhibit large variations in lifetime anddeterioration of electrical properties within relatively short periods.

FIG. 3 illustrates an X-ray diffraction pattern of the dielectricceramic in the monolithic ceramic capacitor of Sample 43, in which theratio of the maximum peak intensity of the secondary crystal phases tothe maximum peak intensity of the perovskite primary crystal phase is11.0%. FIG. 4 illustrates an X-ray diffraction pattern of the dielectricceramic in the monolithic ceramic capacitor of Sample 54, in which theratio is 29.0%. In these drawings, peaks with asterisks (*) are assignedto the perovskite primary crystal phase and other peaks are assigned tothe secondary crystal phases.

In this example, elemental copper was used in the internal electrode ofthe monolithic ceramic capacitor. A copper alloy also has the sameeffects.

As described above, the monolithic ceramic capacitors using the ceramicsbased on the above EXAMPLES exhibit superior electrical properties, thatis, a large CR product of at least 1,000, a small dielectric loss of0.1% or less and a small rate of change in electrostatic resistance withtemperature (TC) of −1,000 ppm/° C. or less.

The mean time to failure (MTTF) in the high-temperature loading lifetimetest is at least 300 hours even when the thickness of the dielectricceramic layer is about 5 μm or less. Moreover, the lifetime of the firstfailed sample is long and the variation in the lifetime between thesamples is small, exhibiting high reliability.

In addition, inexpensive base metals can be used as internal electrodematerials for the monolithic ceramic capacitor. Thus, compact,high-performance monolithic ceramic capacitors can be provided usingelemental nickel or a nickel alloy, or elemental copper or a copperalloy exhibiting superior high-frequency characteristics.

The non-reducing dielectric ceramic of the present invention is usefulas a capacitor material for temperature compensation and a dielectricresonator material for microwaves. The non-reducing dielectric ceramicis also useful as a material for a thin large-capacitance capacitor.

What is claimed is:
 1. A monolithic ceramic capacitor comprising: atleast three dielectric ceramic layers; at least one pair of internalelectrodes each of which is disposed between a different pair ofdielectric ceramic layers; a pair of external electrodes, each of whichis electrically connected to a different one of said pair of internalelectrodes; wherein the dielectric ceramic layers comprise anon-reducing dielectric ceramic comprising Ca, Zr and Ti as metallicelements, free of Pb, and having a perovskite primary crystal phase andother crystal phases; wherein the ratio of the maximum peak intensity ofsecondary crystal phases to the maximum peak intensity at 2θ=25° to 35°of the perovskite primary crystal phase in a CuKα X-ray diffractionpattern is about 12% or less, wherein the secondary crystal phasesinclude all the crystal phases other than the perovskite primary crystalphase; and wherein the internal electrodes comprise a base metal.
 2. Amonolithic ceramic capacitor according to claim 1, wherein the basemetal is at least one member selected from the group consisting ofelemental nickel, a nickel alloy, elemental copper and a copper alloy.3. A monolithic ceramic capacitor according to claim 2, wherein saidratio is about 5% or less.
 4. A monolithic ceramic capacitor accordingto claim 2, wherein said ratio is about 3% or less.
 5. A monolithicceramic capacitor according to claim 1, wherein said ceramic isrepresented by the formula A_(p)BO₃ in which A comprises Ca, B comprisesZr and Ti, and p is about 0.98 to 1.02.
 6. A monolithic ceramiccapacitor according to claim 5, wherein said ratio is about 5% or less.7. A monolithic ceramic capacitor according to claim 5, wherein p isabout 0.99 to 1.01.
 8. A method for making a non-reducing dielectricceramic comprising Ca, Zr and Ti as metallic elements, free of Pb, andhaving a ratio of the maximum peak intensity of secondary crystal phasesto the maximum peak intensity at 20=25° to 35° of a perovskite primarycrystal phase in a CuKα X-ray diffraction pattern of about 12% or less,wherein the secondary crystal phases include all the crystal phasesother than the perovskite primary crystal phase, the method comprisingthe steps of: (A) providing a calcined powder for providing the B-sitecomponent of a dielectric ceramic represented by the general formulaA_(p)BO₃; (B) providing powder for providing the A-site component; (C)mixing the calcined B-site component powder and the A-site componentpowder to prepare an uncalcined primary material powder; (D) calciningthe uncalcined primary material powder to prepare a calcined primarymaterial powder; (E) adjusting the composition of the calcined primarymaterial powder to realize the desired value of p by adding at least oneof the A-site component powder and B-site component powder to thecalcined primary material powder to prepare a secondary material powder;and (F) molding and sintering the secondary material powder under aneutral or reducing atmosphere.
 9. A method for making a non-reducingdielectric ceramic according to claim 8, further comprising calcining aB-site component powder.
 10. A method for making a non-reducingdielectric ceramic according to claim 9, wherein the B-site componentpowder which is calcined has an average particle diameter of about 0.5μm or less.
 11. A method for making a non-reducing dielectric ceramicaccording to claim 9, wherein the uncalcined B-site component powder iscalcined at a temperature of about 1,050° C. to 1,200° C. for 1 to 2hours.
 12. A method for making a non-reducing dielectric ceramicaccording to claim 11, wherein the calcined primary material powder hasan average particle diameter of about 0.8 μm or less.
 13. A method formaking a non-reducing dielectric ceramic according to claim 11, whereinthe provided powders are such that the calcined primary material powderis a ceramic powder having a composition represented by(Ca_(1-v-w)Sr_(v)Ba_(w))_(k)(Zr_(1-x-y)Ti_(x)Hf_(y))O₃ wherein0.95≦k≦1.00, v+w is 0 to less than 1, x is greater than 0, and x+y isless than
 1. 14. A method for making a non-reducing dielectric ceramicaccording to claim 13, wherein the secondary material powder is aceramic powder having a composition represented by(Ca_(1-v-w)Sr_(v)Ba_(w))p(Zr_(1-x-y)Ti_(x)Hf_(y))O₃, and wherein p isadjusted to a value of about 0.98 to 1.02.
 15. A method for making anon-reducing dielectric ceramic according to claim 14, wherein p isadjusted to a value of about 0.98 to 1.02.
 16. A method for making anon-reducing dielectric ceramic according to claim 15, wherein theB-site component powder which is calcined has an average particlediameter of about 0.5 μm or less.